1. Technical Field
The present invention relates to a conveying device and an image forming apparatus.
2. Related Art
An image forming apparatus is known that conveys a recording medium, such as paper, and jets ink droplets onto the recording medium using an inkjet recording head.
In such an image forming apparatus it is necessary to have a small separation distance between the recording medium and the inkjet recording head (for example maintain the separation distance at about 1 mm or less). Consequently, a mechanism is required for retaining the recording medium on a conveying unit (such as a belt or drum), particularly when forming images at high speed.
However, problems of paper deformation (curl) arise when paper that is not of inkjet-specification, such as ordinary coated printing paper and standard plain paper, is employed as the recording medium in an inkjet recording apparatus, and in particular when an ink with water as a solvent is jetted.
Obviously curl is detrimental to output product quality, however there is also the possibility that minute undulations, at a level not discernible by user eye, that occurred when printing the front face subsequently result in the generation of large creases at a tail portion (trailing edge portion) of the paper when printing the back face of the paper. Such creases arise when the paper is restrained by rollers and the undulations are pressed towards and fixed to the surface of the tail portion of the paper adhered the conveying unit.
An image forming apparatus equipped with a press roller for restraining paper is described in Japanese Patent Application Laid-Open (JP-A) No. 9-175685. A configuration is described for the image forming apparatus in which the central portion of paper is pressed harder than the two edge portions due to the central portion of the press roller being fatter than the two end portions, so as not to induce waviness (creasing).
However, when the method of the above document is applied for conveying a paper with a reverse-face thereof facing upward after an image has already been formed on a front-face of the paper by inkjet heads on large size paper (for example Half Kiku size (636 mm×469 mm) or B2 size paper), it is known that the two end portions of the press roller still press the paper, even if only weakly (see paragraph number [0025]), resulting in creases being induced at the central portion of the paper.